294 Mr. Voulton' a further experiments iipon 



A. Introductory. 



My attention was first directed to this subject by 

 the writings of Meldola, and especially his editorial 

 notes to Weismann's ' Studies in the Theory of Descent.' 

 His statements recalled my own early experience of 

 the variations in colour of the larvae of Smerintlius ocel- 

 latns when found on different food-plants. I therefore 

 determined to experiment upon this species and other 

 Spldmiida; which were also known to vary under similar 

 conditions. I first experimented (1884) upon Smerintlius 

 ocellatus and SpJtinx Uf/ustri, and proved that the shade 

 of green can be modified in both these species (Proc. 

 Roy. Soc, No. 237, 1885, p. 269). At the same time 

 I showed that the effect cannot be iDhiitophagic in the 

 strict sense of the word, but rather phytoscopic {I. c, 

 pp. 306 — 308), inasmuch as the colour of the surface 

 of the leaf rather than its substance acts as the stimulus. 

 In 1885 these results were extended and confirmed by 

 further experiments on S. ocellatus (Proc. Roy. Soc, 

 No. 243, 1886, p. 135). For some years I continued 

 working at this species, and expended a vast amount of 

 unproductive labour upon it. At some future time I 

 hope to extract from the voluminous notes of several 

 years' work a comparatively few details which may be 

 of interest. At that time no one believed that this 

 susceptibility was of common occurrence, and could 

 produce far wider differences in many well-known larvae, 

 which were therefore more suited for an investigation 

 into the conditions and limits of the change which 

 takes place. A suggestion made by Lord Walsingham 

 first turned my attention from the Sphingidie in the 

 direction of far better material. This suggestion was 

 that the larvae of Rumia cratcegata, sometimes green and 

 sometimes brown, might perhaps be found susceptible 

 to these influences. I first experimented upon them in 

 1886, and in that and the subsequent years investigated 

 many species of Gcometrce and Nocture. The general 

 results of this work have been very briefly stated from 

 time to time (' Colours of Animals,' Internat. Sci. Series, 

 London, 1890, pp. 150—153, British Assn., 1887, 1892, 

 Trans. Ent. Soc, Lond., &c), but the details have 

 never been given. At the same time, the complete 

 establishment of a princii)le such as this demands the 



